1 24 PHOSPHA TIC MANURES 



(b) Qualitative Examination. — As many organic 

 waste products as are obtainable should be examined, 

 and their general appearance, odour, and other 

 characteristics noted. Particular attention should be 

 paid to the texture, since coarse material is not nearly 

 so valuable as that which is disintegrated. A few of 

 the manures should be subjected to the same qualitative 

 tests as are described for the shoddies, etc. (105, 

 p. 121). 



{c) Analysis. — The analysis follows the same lines 

 as those given for the fibrous wastes, but a larger 

 portion should be used for the nitrogen estimation 

 (about 10 grams), the sulphuric acid digest made up to 

 a definite volume, and aliquot parts taken for the 

 distillation with caustic soda. This reduces the error 

 due to the difficulty of properly sampling very mixed 

 or coarse waste products. 



CHAPTER XII 

 Phosphatic Manures 



With the exception of the phosphates of sodium and potassium, 

 which are occasionally used by market gardeners, etc., all the 

 phosphatic manures in common use are calcium compounds of 

 phosphoric acid, derived either from animal or mineral sources. 

 Phosphoric acid is tribasic, and forms with calcium the com- 

 pounds : — 



Ca3(P04)2 .... Tricalcium or tricalcic phosphate 

 Ca2H2(P04)2 or CaHP04 . Dicalcium hydrogen phosphate 

 CaH4(P04)2 . . . Monocalcium phosphate 



Basic phosphates are also known. * 



The above-named phosphates occur in the different phosphatic 

 fertilisers, sometimes singly, sometimes mixed with one or both of 

 the others. They are distinguished by their solubilities, as 

 follows : — 



